MSE: Increase log visibility when unfragmented MP4 causes parse failure

media/formats/mp4/box_reader.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/formats/mp4/box_reader.h"
 
 #include <string.h>
 #include <algorithm>
 #include <map>
 #include <set>
@@ skipping 204 matching lines @@
 }
 
 bool BoxReader::ReadHeader(bool* err) {
   uint64 size = 0;
   *err = false;
 
   if (!HasBytes(8)) return false;
   CHECK(Read4Into8(&size) && ReadFourCC(&type_));
 
   if (size == 0) {
-    // Media Source specific: we do not support boxes that run to EOS.
+    MEDIA_LOG(DEBUG, log_cb_) << "Media Source Extensions do not support ISO "
+                                 "BMFF boxes that run to EOS";

[chcunningham, 2015/05/15 17:19:33]

I don't know what this means. Why is size 0? 

[wolenetz, 2015/05/15 18:16:25]

:) I was simply log-ifying the previous comment in a drive-by.
I also believe both the previous comment and the log-ified version are correct:
As I understand it from the ISO IEC 14497-12 (2012) spec, section 4.2 (Object
Structure, which describes the pertinent common box header stuff that is parsed
here), there is very specific code in the spec describing that "if (size==0) {
// box extends to end of file }". MSE does not support such boxes in ISO BMFF.
My guess about a use case for something like a box extending to EOS might be an
MDAT containing media data, and whose end is signaled by reaching the end of
media data, rather than the end of the box. This is similar to webm "unknown
cluster lengths" (which *are* supported by MSE due to the nature of block
sequence with Clusters being required to be muxed in DTS sequence, unlike MDAT
in ISO BMFF).

     *err = true;
     return false;
   } else if (size == 1) {
     if (!HasBytes(8)) return false;
     CHECK(Read8(&size));
   }
 
   // Implementation-specific: support for boxes larger than 2^31 has been
   // removed.
   if (size < static_cast<uint64>(pos_) ||
       size > static_cast<uint64>(kint32max)) {
     *err = true;
     return false;
   }
 
   // Note that the pos_ head has advanced to the byte immediately after the
   // header, which is where we want it.
   size_ = size;
   return true;
 }
 
 }  // namespace mp4
 }  // namespace media